From experiments and analyses in the previous report, it was found that element strength distributions (SD_C) obtained by the nonlinear least-squares method (NLM) included a laminating effect. In this report, we validated NLM by comparing 1-ply strength distributions (SD_L) including a laminating effect with SD_C. As the result, NLM was valid for estimating element strength distributions for tension, compression, and bending in the vertical use direction. NLM was also valid for estimating element strength distributions for tension by assuming the criterion that LVL fails by the stress in outermost edge of the tensile side in the horizontal use direction. However, we could not conclude that the NLM was valid for estimating element strength distributions for bending in the horizontal use direction by assuming the criterion that LVL fails by the combined stress in bending and tension in the outermost layer of the tensile side in the horizontal use direction.

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The objective of this study was to investigate the minimum spreading rate for sufficient bonding properties in wood based materials. A device for spreading small amounts was developed by modifying an ink-jet printer with a piezoelectric element. The device permitted the spread of about 5.0 cm³/m² (adhesive liquid base) of water-soluble phenol-formaldehyde resin (PF) adhesive uniformly onto the veneer. The relationships between adhesive spreading rate and bond properties were investigated using birch (Betula spp.) planed veneer and spreading the PF adhesive by the device. A spreading rate of 2.5 g/m² (solid base) of the PF adhesive per single glue line could achieve fully bonding strength with about 100% wood failure at normal conditions. In addition, bonded specimens with a spreading rate of over 7.7 g/m² (solid base) had full durability in a 72-hour continuous boiling test.

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