United States Department of Agriculture Janka Hardness Using Forest Service Nonstandard Specimens Forest Products Laboratory Research David W. Green Note Marshall Begel FPL–RN–0303 William Nelson Abstract Contents Janka hardness determined on 1.5- by 3.5-in. specimens Executive Summary ............................................................. i (2×4s) was found to be equivalent to that determined using Introduction ..........................................................................1 the 2- by 2-in. specimen specified in ASTM D 143. Data are Background ..........................................................................1 presented on the relationship between Janka hardness and History of Standardization ...............................................1 the strength of clear wood. Analysis of historical data de- Relationship of Janka Hardness to Other Properties ........2 termined using standard specimens indicated no difference Strength Properties .......................................................2 between side hardness values determined on the radial face Specific Gravity ...........................................................3 as opposed to the tangential. Analysis of historical data also Load Placement and Specimen Thickness ...................4 indicated that the relationship between hardness modulus Growth Ring Orientation .............................................4 (HM) and Janka hardness (H) may be different for hardwood Moisture Content .........................................................5 species than for softwood. Recommendations are given Hardness Modulus .......................................................6 for ensuring that experimental procedures do not bias the Procedures ............................................................................9 results when testing non-standard specimens. The authors Material ............................................................................9 caution that if hardness (ASTM D 143) and hardness modu- Testing ............................................................................10 lus (ASTM D 1037) are measured simultaneously for each Results and Discussion ......................................................10 ball penetration, the HM /H ratio may be different than that Janka Hardness ...............................................................10 given in D 1037 because the two standards specify different Validity of Individual Values ......................................10 rates of penetration. Analysis of Results ....................................................11 Janka Hardness and Hardness Modulus .........................11 Keywords: Janka hardness, hardness modulus, Douglas-fir, Conclusions ........................................................................12 2×4 References ..........................................................................13 Metric conversion chart Inch–pound unit Conversion factor SI unit Acknowledgments inch (in.) 25.4 millimeter Funding for this study was provided by the Forest Products pound (lb) 0.454 kilogram Laboratory. The authors acknowledge the assistance of Tim- pound–force (lbf) 0.27 Newton othy Nelson of the Forest Products Laboratory for specimen temperature ºF (T − 32)/1.8 temperature ºC F preparation and testing. February 2006 Green, David W.; Begel, Marshall; Nelson, William. 2006. Janka hardness using nonstandard specimens. Research Note FPL-RN-0303. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Labora- tory. 13 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. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright. The use of trade or firm 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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We also found that when using an automated routine to select Background load and deformation points off a continuous electronic re- The Janka ball hardness test has been specified for solid cord, it is important to ensure that the load reported for hard- wood in ASTM standard D 143 since 1922. The standard ness corresponds very closely to a deformation of 0.222 in. calls for a specimen with a cross section of 2 by 2 in. Un- For all thickness values, the data indicated a ratio of hard- like the tests for some properties, this standard does not ness modulus to Janka hardness (HM /H) of 4.9 as opposed provide an alternative size of 1 by 1 in. The standard also to the value of 5.4 given in ASTM D 1037. This difference requires tests on the radial and tangential faces of the speci- was attributed to two factors. First, the D 1037 ratio was men, with the average of the values obtained reported as originally developed by combining data for softwood and the hardness of the specimen. The study presented here was hardwood species. A reanalysis of the historical data indi- prompted by our concerns about the results obtained when cated that whereas a ratio of 5.3 is appropriate for hardwood conducting Janka hardness tests on non-standard specimens. species, the ratio for softwood species should be 4.4. Sec- Hardness tests had been conducted on 1.5- by 3.5-in. speci- ond, the rate of loading specified for Janka hardness in both mens (2×4s) as part of a study of the properties of lumber D 143 and D 1037 is 0.25 in/min, whereas D 1037 specifies cut from small-diameter Douglas-fir trees growing in dense a rate of 0.05 in/min for determining hardness modulus. stands. These two properties can be determined by current specifi- cations only by making two separate indentations for each Objectives property. In our tests, both Janka hardness and hardness Our primary objective was to evaluate hardness values modulus were measured on one indentation, using a rate of determined from tests on 1.5-in.-thick 2×4s compared to indentation of 0.25 in/min and resulted in an HM /H ratio of values that would have been obtained on standard 2-in.- about 4.9. We speculate that had we determined hardness thick specimens. The study included determining the effect modulus at a rate of loading five times slower, then the ratio of thickness on Janka hardness as well as a critical analysis of hardness to hardness modulus would have been lower and of historical data and information on various factors that more in line with the expected result. might affect Janka hardness. Our secondary objective was to provide additional information about the relationship be- Conclusions tween Janka hardness and the hardness modulus specified in From our test results and a critical review of existing litera- ASTM D 1037. ture we conclude the following: Procedures • Hardness values can be determined for 2×4s that are Hardness tests were conducted using indentations on the equivalent to those that would have been obtained by us- wide face of 2×4s at thickness values of 1, 1.5, and 3 in. ing the standard 2- by 2- by 6-in. specimen of ASTM The 1-in. data were obtained by planing the 1.5-in. 2×4 on D 143. the side opposite the indentations; the 3-in. results were ob- • If two pieces must be used to obtained a desired thickness, tained by either “stacking” the specimen to be tested on top the pieces should be glued together. of another 2×4 or by “gluing” the 2×4 to be tested to another • Continuous recording of load and deflection offers oppor- 2×4. The test set-up allowed continuous recording of load as tunities to better understand the results of Janka hardness a function of penetration depth of the standard 0.444-in.-di- tests on wood products, but care must be taken to ensure ameter steel ball into the specimen. Since hardness modulus that the load reported is actually that at 0.222-in. is simply the relationship between the slope of the load and deformation. the penetration depth, it was possible to obtain both Janka • There is no significant difference between hardness deter- hardness and hardness modulus from the same indentation. mined on the radial face as opposed to that determined on the tangential face, even for oak. Results • Reanalysis of historical data indicates