16 



HARDWOOD RECORD 



August 10, i!>.;i 



with each use. Tlie four combinations of mechanical properties, 

 which in most instances will give a good comparison of the different 

 kinds of woods for various uses, are termed in this report, strength 

 as a beam or post, hardness, shock-resisting ability, and stiffness. 



The method of viimbimng the varimin properties is shown in tabic 'J. 

 Each 0} the properties, such us hanlncss, stiffness, etc., which arc men- 

 tioned, is measured liu means tij a eompiisite tUiure. This composite fiyurc 

 is made up hp eumhininti the several test values lohich arc indioative of 

 the prupeity. Each of these values is first multiplied bp a reduction factor 

 in order to reduce or adjust the valiien to approximately the same order of 

 magnitude, /'or instance, modulus of rupture is used as the base to lOhich 

 tlui other values an- reduced in dcririiiii the ■■strength as a beam or post" 

 figure. The uriruge ratio of modulus of rupture to fiber stress at elastie 

 limit in static bending is for green ntnterial l.SO. Then 1.80 is the reduc- 

 tion factor c.pplied to fiber stresx at eldjtt c limit in static bending. The 

 adjusted value resulting from applging similajlg derived factors to each 

 individual value is then multiplied bp a weighting factor. This weighting 

 factor represents approximately the relative importance of the value as 

 well as the relative iwcuraey of the determination of that value and takes 

 into account the relative number of tests muAlc in obtaining the values. 

 Results of tests on both green and air-dry material arc used. The results 

 on green material, because of the greater number of tests, arc given tteiee 

 as much weight as results on air-dry 7natcrial. The results from tests of 

 air-dry material are adjusted to TJ per cent moisture before being cwn- 

 binrd into the ct.mposite figure. The sum of the prttducts of test value by 

 reduction factor by we ghting factor is dirided hy the .sum of the weighting 



factors. The quotient is the composite figure. J his method of eombimiig 

 individual tests renders the data less valuable for detailed application, 

 hut more valuable for a general comparison of species when eompostie 

 figures are available for the different species. 



Table 3*was derived by obtaining the L-oiicjiosite figures for 

 shrinkage in volume from green to oven-dry condition, oven-dry 

 .specific gravity based on volume when green, strength as a beam or 

 post, hardness, shock-resisting ability, and stiffness, for the dif- 

 ferent woods, and then comparing each property of each wood with 

 the composite figure of the same i)roperty for oak; hence, for these 

 jiroperties it is a table of relative percentages based on oak as lOU 

 jicr cent. In addition, the actual weights per cubic foot of green, 

 air-dried and kiln-dried wood, radial and tangential shrinkage, and 

 the ratio of the tangential to the radi.'il shrinkage are given. 



Considering the properties of oak, it may be stated that they 

 show considerable variations. This is due to a slight extent to 

 differences between thi' numerous species, but primarily to differ- 



•Indiviiliial properties l"roni which these euniljliiations lire made are 

 t;iven in I'lilteil States Department of ARrieulture Bulletin No. 55t>, 

 entitled. ".Mechanical I'roperties of Woods Crown in the- United .States." 

 l),v .1. A. i ewlin an. I T. H. I'. Wilson, 1!<]7. 



