Three methods were devised to measure the hardness of small wood samples: a sanding test, a diamond point indentation test, and a saw blade tooth deformity test. Based on step-wise multiple regression analysis with 19 and with five important independent variables, the sanding test was best, followed by the indentation test. The saw blade test gave poor results and was discarded. The order of important independent variables among the four plots analyzed individually showed a nearly perfect relationship with the sanding test, but no consistent order of the variables among plots for the indentation test. Again this indicated that the sanding test was best

Hamilton, John R.

Litwin, Paul J.

Renton, John J.

Tryon, Earl H.

English

Wood and Fiber Science (E-Journal)

THREE METHODS O F  DETERMINING HARDNESS O F  INCREMENT CORE SEGMENTS' E a ~ l  H .  Tryon  Profcssor of Silvicultnre, Division of Forcstry West Virginia University, Morganto\vn, West Virginia 26506 Paul J. Litujin Instn~ctor of Fortast~y, Fox Valley Technical Institute 1825 North Bh~en lo~md Drive, Appleton, Wisconsin 54911 John R. Hamilton l'rofrssor of Wood Science, Division of Forestry West Virginia University, Morgantolvn, West Virginia 26506 and Jo11n J .  Renton" Profcssor of Geology, White Hall West Virginia University, Morgantown, West Virginia 20506 ARSTIZACT Three methods were devised to nlcasure the hardness of s~iiall wood samples: a sanding test, a dia~nond point indentation test, and a saw blade tooth defo~mity test. Based on step- wise multiplc regression analysis with 19 and with five iinportant independent variables, thct sanding test was best, follo\ved 114. the indentation test. The saw blade test gave poor res111ts and was discarded. The ordcr of important independent variables ;rmong the fonr plots analyzed individually showed a nearly perfect relationship with the sanding test, but no consistent order of the varia1)lcs among plots for the indentation test. Again this indicated that the sanding test was best. Atlrlitionul keywortls: Qt~ercris ruhrn, hardnrss tests, sanding, tool wear, sawing, m;~chining. 0l)servations on the U. S. Forest Service's Fernow Experimental Forcst at Parsons, \Vest Virginia, indicatecl that l u m b e r  sawn from trees gro\vn on li~nestone soils dulled s;iws faster than did lumber fron-I trees grown on sandstone soils. This observation set in motion a project to learn if wood from limestone soils actually had properties that dulled sarv blade teeth faster than \vood fro111 sandstone soils, and if so, to lPul)lishecl with the approval of the West Virginia University Agricnltnral Experiment Station as Scientific Papcr No. 1416. T h e  a~~t l iors  wish to acknowledge the consider- al)lc help of IIarold V. Fairl,ai&s, Professor of hlrtall~irgical Engineering, in devising possible tc.sts for detcri~~iiling hardness of small wood sam- pl(>s; i ~ n d  Stanley Wearden, Professor of Statistics a ~ ~ c l  (:ol~ipr~tc>r Scicnc?, \vho gl~ided the statistical tcssts 11sec1 to deter~rrine lwst ~rr~tliods.  Rot11 scien- ti\ts arca at  Wt,st Virginiil [Tnivc~rsity. learn what wood properties were respon- sible. Preliminary to the main study, a method had to be selected, or developed, to test the "hardness" of wood. The method would need to be suitable for testing small wood ., sai~rples because increment cores would be used rather than lumber due to the rel- atively Luge number of trees needed and the difficulty of obtaining lumber from trees from the sites se1ect;d. The purpose of this paper is to present the procedure used in developing a method for testing the "hardness" of small wood samples. Four areas in northern West Virginia were selected for study. They were in even-aged linrrl\~~ood stands with abundant \ \  0 0 1 )  Ah11 FII3ElI 287 WINTER 197fi, V. 7 ( 4 )  288 I':AII~. R. TRYON *:'I' AL.. I?I(:. I .  S;~ntling tcst apparatus ( t o p )  ; ~ n d  sa\v I~latle test apparatus (I~otto~n).  L1AHI)Nk:SS OF IVCRIChIEN'r CORE bl.:(:XIL.:NTS 289 FK:. 2. Photograph of .;anr 11lade iinagtxs taken before and after saving. The stnallest units are in ~ ~ ~ i l l i ~ ~ ~ t ~ t c ~ r s .  11orthvr11 retl oak ( Querclis rzil~rt~ L. ) rang- i11g i l l  agc fro111 35 to 60 years. Two areas wrrc on limc~stone-deri~ied soils, and two were on sandstone-derived soils. 0 1 1  each rock type, one area was moist and thc: other dry. Twenty dominant red oaks were ran- tlomly selected on cuch of the four areas. Two incre~nent cores, 5 inill ill diameter, were taken near tl.l~.ll. fro111 each oak. The I ~ C  were two cores extencled to the pith, v 1 o11 the same radius about two iilch(:s apart vertically. One core was ashecl for ele- ~neiltal :ii~alysis. From the other core, a six- ri11g segiuent, having utlifornl ring widths, and includi~lg the 20th to 25th annual rings from tllc pith was selected for testing for hardness. Iiardness and abrasive resistance were co~lsidered to have the greatest correlation with tooth wear. Hardness is defined as resistance to indentatioil and is con~monly determined by the Janka test, involving resistance to indentation using a 0.444-inch- diameter steel ball (A.S.T.M. 1965; CSDA Forest Products Lab. 1974). Abrasive re- sistance refers to the ability of a substance to resist the weari~lg away of a surface when rub1)ecl across thc surface of another sub- stance (Ilechtlinger 1959). Three nlethods were finally devised to test the snlall wood samples: (1) a sanding test, ( 2 )  a dia~llolld point indentation test, and ( 3 )  a saw blade test. The first one, sanding, was considered to measure a h a -  sivc resistance, and the others to ineasure hardness. However, all three will be called hardness tests for sinlplicity in presentation. %x) EARL H. TRYON ET AL. A Santling Test was developed which used a four-inch width of aluminum oxide sanding paper, grit size 80 D, as the z~bracl- ing surface, over which a weighed incrc- ment core segment was drawn. The place- ment of the sandpaper, a guide, aucl the specimen holding apparatus weighing 485 grams rnay be seen in Fig. 1. The incre- ment core segment with wood fibers per- pendicular to the sanding surface was pulled across the sandpaper 100 strokes per segment, or 400 inches of total ab1.7 c ~1011. ' A fresh sanding surface was used for each stroke. The percentage of oven-dry weight loss by sanding was used as a measure of hardness. The greater the weight loss, the softer the wood was considered to be. This test, as well as the other two, was made with the s:imples at a uniform moisture con- tent, oven-dry at the start of each test. A Diamond Point Indentation Test was u s ~ d  which was considered to produce sim- ilar, but not identical, results as the stan- dard Janka test for hardness. Each segment was mounted on a wooden block, sanded to ol~tain a smooth, flat surface, and brought to a linifornl moisture content in a desiccator jar in the testing room. The sample was then placed on the Tukon Hardness 'Tester, hlodcl M.O. (Freudenthal 1950), and with a 100-gram load, two diamond-shaped in- dentations were made in the, transverse plane of the summer wood of each of the six ni~nual rings of each seg~nent. The dis- tances froin one apex to another across the indentations were measured using a vertical illumination system with a 40X objective and a 1 0 ~  eyepiece. Indentation lengths could be measurcd from 5 to over 1,000 ~nicrons. The distance across the inclenta- tions should be inversely related to hard- ness. A Sazc Blate Toot11 Deformity Test was devised using as a basis the fact that the harder the wood the greater would be the deformity imparted to the teeth when drawn across the wood. Saw blades were made from 0.012-inch-thick 1100 aluminum alloy ( A.S.T.M. Standards ) having 99% ininimum aluminum. The teeth of the blades were formed by filing while being  TAB^ 1. RZ U U ~ Z ~ ~ S  tiset1 a.c a criteria in selecting trsahle I~arthre.ss test for red oak increment core .segments - - -- -- - - - -- -. . - . . . . . . - -. . . . . . . . . . . . . . - . . - T e s t  R~ o f  t w e n t y  R~ o f  f i v e  v a r i a b l e  e q u a t i o n  v a r i a b l e  e q u a t i o n  -- - - - -- - - --- Sanding  0.8491 0.8101 I n d e n t a t i o n  0.4144 0.4002 Saw b l a d e  0.3771 0.2301 .. -- ~ ~ held in a forin. The finished blades were tensioned as uniformly by hand as possible in a jeweler's saw frame, this assembly with weights weighing approximately 180 grams. The tests were made in the summer wood of the 25th ring from the pith for each sam- ple. A device was made to hold the core segments and guide the saw (Fig. 1 ) .  A total of 150 strokes, pulled in one direction only by hand at a uniform velocity across the tangential surface of the 25th ring, was made using a separate blade for each sani- ple. The length of each strokc was about 40 millimeters. The technique used to de- termine tooth defornlation involved photo- graphic double exposures before and after the test. These are shown in Fig. 2. The difference in the number of units represent- ing teeth heights before and after the test indicates the amomlt of saw teeth displace- ment, or the hardness of the wood. Multiple regression arlalyses with the stepwise elimination of variables were used for evaluating the three hardness tests. Nineteen independent variables were in- volved in the testing. They included: rock type, site index, specific gravity, sample length, percent latewood of sample, percent latewood of 25th year, vigor index, rings per inch, width of 25th year; and the elemental constituents as percentages of the elemental ash analysis: SiO-, Fez03, Al&, CaC03, MgCo3, MnO, NiO, CuO, Cr203, and PbO. I11 addition, plot-by-plot stepwise mul- tiple regression analyses were run to help evaluate the three testing methods. The percentage of variability explained (K') by an individual multiple rcgression equation was used to evaluate the reliability of the IIAllDNESS OF INCHEhlENT CORE SE(;hll':NTS 291 ' I I  2 S ~ I I ( ( ~ I I ~  t . 5 t  .sfatisti~al data of the ~1ot -hy- f ) lo t  ~ n ~ r l t i p l e  r gression ~irralyses used us a e ~ i t e ~ i a  it1 hardness testing - - - ~  ~ ------ --  -- - . ~ ~~~ - ~~~ - - - -- -- - . -- .~- . . o r d e r o f  i!qPPCtd"ce-cc vd-ri ah! es a. I ' l o t  R N o s t  L e a s t  5 ,1nds t .o1 ie ,  d r y  s i t e  0 . 9 5 1 8  R * *  S * *  V C a  I i ~ l l c i t o r l e ,  d r y  s i t e  0.:;565 R * *  S * Ca V ' R = r i n q i  p e r  i l ~ c h  5 = s p e c i f i c  g r a v i t y  '1 = v i g o r  i n d e x  C a  - I r ~ r c e t i t  C a C U 3  thrce I1iirdness tests, with the greatest R2 value used to indicate the best method. An It+valuc> of 0.50 was considered an accept- ahle ininimmn, as is commonly uscd in testing biologicit1 data. Also, the order of irn- portance of the strongest independent vari- al)lcs :iiitl their similarity anlong plots for each test \vas used to complement the re- sults of thc initial multiple regression anal- yses. The basis for such a comparison is the Friedinan nonparametric test (Siege1 1956); however, bccause of the highly sig- ~rificnnt nature of the order of the variables, thc actual tests \yere not necessary. IIESULTS AND DISCUSSION The results of tlie multiple regression tests for the original 20-variable and the five-most-important-varinble equ a t' ions are presented in Table 1. The sanding test clearly had the greatest R"11 b'otli equa- tions, exceeding 0.8 in both instances, and was well above the 0.5 It%requirerr~ent for an acceptal~le hardness testing method. The illdentation test with R b a l u e s  of 0.4144 and 0.4002 ~vas  considered margin:~I, but tlie saw blade test \vith values of 0.3771 F IT^ 0.2301 indicated snch poor reliability tliat it was dropped from further consider- ation. ** = s i g n i f i c a n t  a t  1  l e v e l  * = s i g n i f i c a n t  a t  5 ' ,  l e v e l  Plot-by-plot inultiple regression analyses \Irere run for the sanding and indentation tests (Tables 2 and 3 ) .  The R' values for tlie sanding test remained high, ranging from 0.7028 to 0.9518. Also, the R+alues for the indentation test were below the arbi- trary 0.5 requirement, ranging from 0.3489 to 0.4366. Thus the plot-by-plot and initial multiple regression analyses were in close agreement. Finally, thc individual variables were studied to determine consistency in order of importance f1.0111 plot to plot. Table 2 shows close agreement of the important variables for the sanding test. The same four vari- ables were most important in each of the four plots, and in three of the four plots the order was exactly the same. In studying the order of important variables in the indenta- tion test, thc five explaining the greatest percentages of variability were used (Table 3 ) .  The same five variables were most im- portant in each of the four plots, but there was no uniformity of the arrangement of the variables fro111 plot to plot. The greater uniformity of order of iinportai~ce of vari- ables in the sanding test as compared with the indentation test, again points to the sanding test as the better inethod of de- termining wood hardness. 292 EARI. H. TRYON ET AL. TAI<LE 3. Iittlentation test statistical data of the plot-by-/,lot inclEti/~le regression a11u1yse.s 1tsei1 as a criteria in hnrt1ne.s~ testing O r d e r  o f  i ~ n p o r t a n c e  o f  v a r i a b l e s a  p l o t  R* ~ o s t  L e a s t  - - .~  ---- . S a n d s t o n e ,  d r y  s i t e  0 . 3 5 5 1  L  5 C a N i P b S a n d s t o n e ,  n l o i s t  s i t e  0 . 4 0 1 6  S * *  14 i P b C a L L i , ~ ~ e s t o n e ,  d r y  s 1  t e  0 . 4 3 6 5  C a  P b S  N i I L i ~ ~ ~ e s t o n c ,  1 1 1 o 1 s t  s i t e  0 . 3 4 8 9  Fl i 5 L  P h C a " = = p e r c e n t  l a t e w o o d  S = s p e c i f i c  g r a v i t y  C a  = p e r ~ e n t  C a C 0 3  I I i  = p e r c c n t  I I i O  P b  - p e r - r e l i t  PhO Origillally the length of the i~lcrenlent core segments was not included in the sand- ing test analysis. However, a ci~rvilinear relationship developed because of a con- stant weight load and varying sarnple lengths. Therefore length was included as an independent variable. The sanding test colild perhaps be improved by using sam- ples of eclual length, and square in cross section rather than round. CONCLUSIONS Methods for assessing hardness were de- vised for use with sillall wood san~ples. The most appropriate test was a s a ~ ~ d i n g  tcst which, on the basis of stepwise multiple regression analysis and ranking of iadepen- dent vai-iableq, appeared to be a better tnethod than either an indentation or saw I~lade deformation test. Possible improve- ~~lei l ts  in the method could include  sing **  = s i g n i f i c a n t  a t  1 p e r c e n t  l e v e l  wood specimens of eclual length rather than having ecp~al numbers of annual rings, and sqliare in cross section instead of round as are increment cores. REFERENCES .4.S.T.M. 1965. S~tanda1.d methods of testing small clear specilllens of timber. Am. Soc. Test. Mater., Des. D143-52 (reapproved 1965 ) . Philadelphia, PA. FKEUDENTHAL, ALFRED M. 1950. The inelastic behavior of engineering materials and struc- tures. John Wiley and Sons, Inc. N.Y. (chap- tclr 18) .  xvi f 587 pp. IIE~IITLIN~:ER, A. 1959. Llodcr11 sciencc dictio- nary. Franklin Publishing Co., Inc. Palisade, New Jersey. 784 pp. SIEGEL, SIDNEY. 1956. Nonparainetric statistics for the behaviorial sciences. McGraw-Hill Book Co., Inc. New York. xvii + 312 pp. LT. S. FOREST PROUUCTS LABORATORY. 1973. Wood handbook: wood as an engineering material. U.S.D.A. Agric. Handbook 72, rev. 

Three Methods of Determining Hardness of Increment Core Segments

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Three Methods of Determining Hardness of Increment Core Segments

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