Nondestructive evaluation of modulus of elasticity of yellow-poplar LVL: effect of veneer-joint design and relative humidity.

摘要

Two non-destructive testing (NDT) methods, stress-wave propagation and transverse vibration, were employed to evaluate the modulus of elasticity (MOE) of laminated veneer lumber (LVL) fabricated with rotary-peeled yellow-poplar (YP) veneers and phenol-formaldehyde resin. Three groups of LVL specimens, 50 in each group, randomly selected from a very large sample population (over 250), were evaluated in this study. Group I specimens had scarfed veneer-joints; group II had crushed-lap veneer-joints; and group III had no veneer-joints and served as controls. Twenty-five specimens in each group were pre-conditioned and equilibrated under environmental conditions of 65% relative humidity (RH) and the remainder under 95% RH at 23.9℃ (75鳩) before the evaluation of non-destructive MOE. Results showed that MOEs of YP-LVL predicted by NDT methods were influenced by the presence of veneer-joints and the difference existed between the NDT methods used. The RH effect was not accurately demonstrated by both NDT methods except in the group without veneer-joints. Significant increase of moisture content (MC) in the LVLs resulted from the increase of RH, but change in densities of LVLs was relatively small. Analysis of correlation between NDT MOEs and the static bending MOE was performed, and poor to fair correlations were observed under the condition of 65% RH.