United States Department of Agriculture Estimating Janka Forest Service Forest Hardness from Speci¿ c Products Laboratory Gravity for Tropical and Research Paper FPL-RP-643 Temperate Species Michael C. Wiemann David W. Green Abstract Contents Using mean values for basic (green) specific gravity and Page Janka side hardness for individual species obtained from Executive Summary ............................................................. i the world literature, regression equations were developed to predict side hardness from specific gravity. Statistical Introduction .......................................................................... 1 and graphical methods showed that the hardness–specific Background .......................................................................... 1 gravity relationship is the same for tropical and temperate Materials and Methods .........................................................2 hardwoods, but that the relationship for softwoods is dif- ferent from that for hardwoods. As expected, the relation- Specific Gravity and Hardness Definitions .....................2 ship for green wood is different from that for wood at 12% Data Sources ................................................................... 3 moisture content. Separation of Data into Groupings ................................. 3 Keywords: Janka hardness, specific gravity, temperate Selection of Model Form ................................................. 3 hardwoods, tropical hardwoods, softwoods Data Analysis ................................................................... 4 Acknowledgments Results .................................................................................. 4 Funding for this study was provided by the Forest Products Development of Predictive Equations ............................ 4 Laboratory. The authors are grateful for the reviews of Matt Adequacy of the Fit .........................................................7 Myers (Armstrong World Industries), James P. Armstrong (West Virginia University), and David E. Kretschmann Discussion ............................................................................ 8 (Forest Products Laboratory). Modeling Property–Specific Gravity Relationships ....... 8 Predictive Equations Based on Specific Gravity at 12% MC ...................................................................... 9 Effect of MC on Hardness ............................................ 10 Conclusions ........................................................................ 11 Literature Cited .................................................................. 11 Appendix 1—Specific Gravity, Side Hardness, Number of Trees Sampled, and Sources of Data for Species Used to Derive Equations (1) to (8) ............................................ 14 Appendix 2—Specific Gravity, Side Hardness, and Sources of Data for Species Not Used in the Derivations September 2007 of the Equations ................................................................. 20 Appendix 3—Meyer hardness (H ) as a function of MC Wiemann, Michael C.; Green, David W. 2007. Estimating Janka hardness M from speci¿ c gravity for tropical and temperate species. Research Paper (Sekiya 1936) .....................................................................21 FPL-RP-643. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 21 p. A limited number of free copies of this publication are available to the public from the Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53726–2398. This publication is also available online at www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries in the United States and elsewhere. The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. The use of trade or ¿ rm names in this publication is for reader information and does not imply endorsement by the United States Department of Agriculture (USDA) of any product or service. 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Executive Summary Discussion Background The equations for hardness at 12% MC given above differ from those historically used in the Wood Handbook. The There is increasing interest in using species from foreign Wood Handbook equations relating hardness to speci¿ c origins, especially tropical hardwoods, for À ooring. The gravity for dry wood have traditionally been based on hard- Wood Handbook (FPL 1999) contains side hardness values ness and speci¿ c gravity determined at 12% MC (G .) The obtained by the Janka test procedure for most domestic spe- 12 equations for dry lumber given above are based on hardness cies and for almost 80 species commonly imported into the at 12% MC and speci¿ c gravity when green. These equa- United States from countries other than Canada. However, tions may be converted to the G form using adjustment there are beginning to be more requests for hardness values 12 procedures given in ASTM D 2395-02 (2006). Using these for foreign species for which we do not have Janka hardness adjustments, Equations (5b) and (8b) become results. The Wood Handbook also has equations that can be used to estimate Janka hardness from speci¿ c gravity. These 12% hardness, temperate softwoods equations were derived from data on domestic species and H(lbf) = 2,560(G12/(1+0.162G12)) do not contain species with speci¿ c gravity values as high as 12% hardness, all hardwoods those of many tropical hardwoods. H(lbf) = 4,090(G12/(1+0.162G12)) Objective where H is given in pounds force and G12 is speci¿ c gravity The objective of this study was to develop equations relating based on ovendry weight and volume at 12% MC. Janka hardness to speci¿ c gravity for both temperate and tropical hardwoods and temperate softwoods. Conclusions Materials and Methods 1. The variability (range and standard deviation) of spe- ci¿ c gravity for temperate softwoods is less than that of Basic speci¿ c gravity, also called green speci¿ c gravity temperate hardwoods and much less than that of tropical (Gg), is the ovendry weight of a sample divided by the hardwoods. weight of water displaced by the sample’s green volume. 2. The hardness of dry wood is greater than that of green Because it is calculated from the maximum volume and wood. For temperate softwoods, this increase is about minimum weight, the speci¿ c gravity is less variable than 43%; for temperate hardwoods, it is about 31%; and for speci¿ c gravity values calculated using the weight of dis- tropical hardwoods, it is about 26%. placed water at other moisture contents (MCs). Data on the 3. For both green and dry wood, the relationship between mean side hardness and mean Gg for 237 hardwood and 47 hardness and speci¿ c gravity of temperate softwoods is softwood species was taken from the Wood Handbook and different from that of hardwoods. other world literature (Appendix 1). Power models of the 4. For both green and dry wood, the relationship between b form Hardness = a(Gg) were ¿ t to these data. hardness and speci¿ c gravity of temperate hardwoods Results does not differ from that of tropical hardwoods. Thus the The side hardness–speci¿ c gravity relationships determined recommended estimation equations are Equations (1b) in this study are as follows. (Equation numbers are the same and (4b) for green wood and Equations (5b) and (8b) for as those given in the text; the suf¿ x “b” indicates the coef- wood at 12% MC. ¿ cient is for pounds force (lbf) rather than newtons (N).) Green hardness, temperate softwoods 1.50 2 H(lbf) = 1,560(Gg) r = 0.70 (1b) Green hardness, temperate hardwoods 2.17 2 H(lbf) = 3,500(Gg) r = 0.91 (2b) Green hardness, tropical hardwoods 1.91 2 H(lbf) = 3,000(Gg) r = 0.90 (3b) Green hardness, all hardwoods 1.96 2 H(lbf) = 3,060(Gg) r = 0.90 (4b) 12% hardness, temperate softwoods 1.65 2 H(lbf) = 2,560(Gg) r = 0.73 (5b) 12% hardness, temperate hardwoods 2.14 2 H(lbf) = 4,470(Gg) r = 0.91 (6b) 12% hardness, tropical hardwoods 2.06 2 H(lbf) = 4,040(Gg) r = 0.94 (7b) 12% hardness, all hardwoods 2.05 2 H(lbf) = 4,090(Gg) r = 0.93 (8b) Estimating Janka Hardness from Specific Gravity for Tropical and Temperate Species Michael C. Wiemann, Botanist David W. Green, Research Engineer Emeritus Forest Products Laboratory, Madison, Wisconsin Introduction In the United States, Janka hardness (ASTM D 143-94 (ASTM 2006)) was initially used as a minimally destruc- tive test for estimating the strength and stiffness properties of wood (Green et al. 2006). Currently side hardness, de- termined using the Janka test, is a primary method used to assess the suitability of wood species for use as residential and commercial À ooring. The Wood Handbook