Effect of Growth Rings Per Inch and Specific Gravity on Compression Perpendicular to Grain in No. 2: 2 by 8 and 2 by 10 Southern Pine Lumber

Southern pine lumber 2 by 8s and 2 by 10s from across the Southeast were used as the parent material source for this study. Fundamental data were collected for each piece of lumber: growth rings per inch (RPI), presence of pith, and specific gravity (SG), among other information. After mechanical property evaluation through static bending, small clear specimens were cut from the lumber pieces and tested for compression perpendicular to grain (C⊥). Those values were then compared with 2 by 8 and 2 by 10 average RPI and density. The results were significant for both tests. Therefore, a segmentation of the growth ring data into groups of <3, 3 to 5, and >5 RPI was conducted. Correlations were run specific to each group, per both lumber sizes, and still significance was found. Segmentation of SG was not significant only for 2 by 8 SG <0.4. The results suggest that SG is a better predictor of C⊥ than RPI alone due to statistical significance found during these analyses.

Effect of growth rings per inch and density on compression parallel to grain in southern pine lumber

The objective of this study was to evaluate the relationship of growth characteristics to compression properties from commercially available southern pine lumber. The in-grade No. 2 southern pine lumber was collected from retail stores across the Southeast United States. For this specific project, 797 samples of 2 × 8 and 2 × 10 boards were examined. The samples were subjected to static bending following ASTM D 198 to determine mechanical properties. The 2 × 8 samples averaged 4.78 growth rings per inch (RPI) and the 2 × 10s averaged 3.95. Average density (ρ) was 477 kg·m-3 in the 2 × 8 and 487 kg·m-3 for the 2 × 10 specimens. From small clear samples from the parent boards, compression parallel to grain averaged from 43.78 MPa for the 2 × 8 to 46.77 MPa for the 2 × 10. Correlations were run to test significance among growth rings per inch and compressions parallel to grain, across both sizes: 2 × 8 and 2 × 10. Slight significance was found in those correlations and increased in measure from 2 × 8 to 2 × 10. The segmentation of RPI into three distinct groups helped strengthen the findings of effect on compression parallel to grain. Moreover, the addition of density as another test variable further strengthened in relationship per those RPI categorizations. Statistically significant findings for density per RPI segments, R2 values: for 2 × 8 equal 0.31 (3 or less RPI) to 0.60 (more than 5 RPI). For the 2 × 10 lumber per the same segments, R2 values: 0.39, 0.46 and 0.25, respectively. The results suggest ρ is a better predictor than RPI alone for compression parallel to grain values.

Correlations between Grain Angle Meter Readings and Bending Properties of Mill-Run Southern Pine Lumber

Metriguard's grain angle meter (Model 511) measures grain angle in wood by assessing permittivity. This study evaluates the correlations between grain angle meter readings and bending properties of 1,400 kiln-dried 2 by 4 specimens of southern pine (Pinus spp.) lumber and considers its utility for providing supplementary data for predicting the strength of lumber. The results showed that in mill-run lumber, the correlation between grain angle and modulus of rupture (MOR) was −0.420. In addition, in graded lumber, the correlation between grain angle and MOR got progressively stronger as the grade went down. With a few technical modifications, applying this device in a mill production setting could prove useful for supplementing other nondestructive methods for assessing bending strength in lumber.

Nondestructive Evaluation of 2 by 8 and 2 by 10 Southern Pine Dimensional Lumber

This study investigated the use of two nondestructive testing (NDT) methods to evaluate the mechanical properties of No. 2 grade: 2 by 8 and 2 by 10 southern pine lumber. The dynamic modulus of elasticity (dMOE) of each specimen was evaluated nondestructively by using longitudinal vibration and transverse vibration in edgewise and flatwise directions. After the NDT evaluation, the specimens were destructively tested and correlations between static bending MOE with modulus of rupture (MOR) and dMOE were developed. The overall MOE values were 11.14 and 10.96 GPa for 2 by 8 and 2 by 10, respectively. For MOR, the overall value for 2 by 8 was 42.59 MPa, and for 2 by 10 was 43.05 MPa. As expected, results showed statistically significant correlations between static MOE and dMOE (with r ranging from 0.87 to 0.96 for both sizes tested). Also as expected, weaker correlations were found between MOR and the dMOE values (with r ranging from 0.42 to 0.57 for both sizes tested). The lower correlations are largely explained by the difference between the NDT tools analyzing each specimen's global stiffness versus MOR, which is influenced heavily by localized characteristics. Perhaps this finding occurred because larger strength-reducing characteristics are permitted in larger section pieces (2 by 8 vs. 2 by 10) and thus they have opportunity for greater variability. The continuation of studies to develop more reliable NDT is crucial to improve the evaluation of mechanical properties of southern pine lumber and is beneficial to the southern pine timber industry.

The Effect of Multiple Knots in Close Proximity on Southern Pine Lumber Properties

Lumber grade rules address well-spaced single-knot and combination-knot sizes. Information is lacking, however, with respect to multiple knots in close proximity. The term “well-spaced” appears to lack quantitation. This research investigates the effect that knots in close proximity (not necessarily combination knots) have on the strength properties of southern yellow pine (SYP; Pinus spp.) lumber. This study attempts to use a statistical model to determine the modulus of rupture (MOR) for SYP having multiple knots in close proximity using variables including the knot diameter (KD), amount of clear wood (CW) present, knot area (KA), and modulus of elasticity (MOE) of the lumber. This study investigated specimens of 2 by 4-inch SYP dimensional lumber exhibiting multiple knots in close proximity. The basic density (D) was determined by dividing the entire specimen weight by its volume. Third-point bending tests were used in flatwise orientation to quantify the MOR and MOE. There were significant correlations among all parameters analyzed. Multiple regression analysis with one dependent variable, MOR, and three independent variables, KD, MOE, and D, resulted in a coefficient of determination value (r2) of 0.702. When using only the MOE to predict MOR, an r2 value of 0.564 was found.