Jh. Pu et Rc. Tang, NONDESTRUCTIVE EVALUATION OF MODULUS OF ELASTICITY OF SOUTHERN PINE LVL - EFFECT OF VENEER GRADE AND RELATIVE-HUMIDITY, Wood and fiber science, 29(3), 1997, pp. 249-263
Citations number
42
Categorie Soggetti
Materiales Science, Textiles","Materials Science, Paper & Wood",Forestry
Nondestructive testing (NDT) methods, stress-wave propagation, and tra
nsverse vibration were used to evaluate the modulus of elasticity (MOE
) of laminated veneer lumber (LVL). Five types of LVL, fabricated with
southern pine veneers of B, C, and D grades and liquid phenolic forma
ldehyde adhesive, were tested flatwise at environmental conditions of
65% and 95% relative humidity (RH) and 75 degrees F (23.9 degrees C) t
o examine the influence of veneer grade and RH on some nondestructive
mechanical properties of LVL. All LVLs, 1.5 in. (3.81 cm) thick x 3.5
in. (8.89 cm) high x 96 in. (243.84 cm) long, consisted of 13 plies of
southern pine veneer, and their structural designs were: (I) all B gr
ade veneers, (II) 2 plies of B grade veneer on both faces and all C gr
ade veneers in the core plies, (III) 2 plies of B grade veneer on both
faces and all D grade veneer in the core plies, (IV) all C grade vene
ers, and (V) all D grade veneers. Results indicated that MOE of LVL pr
edicted by NDT was influenced by the veneer grade, and specimens fabri
cated with better grade veneers showed a higher value of MOE. A signif
icant decrease in the MOE determined by both NDT methods was found whe
n RH increased from 65% to 95% at 23.9 degrees C (75 degrees F). The M
OE measured by the stress-wave method was found to be more sensitive t
o the RH change than that determined by the transverse-vibration metho
d. A lognormal distribution accurately described the distributions of
MOEs determined by both nondestructive methods at both RH levels. As e
xpected, a significant increase in moisture content (MC) in the LVL re
sulted from increasing RH levels. However, changes in densities of the
tested materials due to the RH changes were found to be smaller. Resu
lts also indicated that regardless of the RH level, MOE determined fro
m the stress-wave test was consistently higher than that obtained from
the transverse-vibration test. For comparison, the results of tests o
n southern pine No. 1 and No. 2 grade lumber, commonly used in light-f
rame construction, are also presented. Analysis of the correlation bet
ween the static bending and NDT MOEs was made and results suggested th
at edgewise static bending MOE of LVL can be predicted with reasonable
accuracy by the stress-wave testing. Good correlations were not obser
ved between the edgewise static bending MOE and the nondestructive MOE
evaluated by flatwise transverse vibration. However, excellent correl
ations between static bending and both NDT MOEs were observed in south
ern pine dimension lumber. Correlations between the MOEs evaluated by
both nondestructive methods were found to be fair for LVL specimens.