. Wood and forest . mber is to besubjected to cross strain, thatis the lower half under tensionand the u]i]ier half under com-]>ression, a knot or other cross-grained portion should be in the u|)pcr half. Strength also includes the ability to resist sheai. This is calledshearing strcngtli. It is a measure of the adhesion of one part ofthe wood to an adjoining jiart. Shearing is what takes place wlienthe portion of wood beyond a mortise near the end of a B C P, Fig. 43, is forced out liy the tenon. In this case it wouldbe shcaiing along the grain, sometimes calleil detvusion. The re
. Wood and forest . mber is to besubjected to cross strain, thatis the lower half under tensionand the u]i]ier half under com-]>ression, a knot or other cross-grained portion should be in the u|)pcr half. Strength also includes the ability to resist sheai. This is calledshearing strcngtli. It is a measure of the adhesion of one part ofthe wood to an adjoining jiart. Shearing is what takes place wlienthe portion of wood beyond a mortise near the end of a B C P, Fig. 43, is forced out liy the tenon. In this case it wouldbe shcaiing along the grain, sometimes calleil detvusion. The resist-ance of the ]W)rtion A B C P, ■/. c. its power of adhesion to the woodadjacent to it on botli sides, is its sbeaiing strength. If the mortisedpiece were forced d(nward until it broke off the tenon at the shoul-der, tliat ^^ould be shearing across the grain. TJie shearing resistanceeither with or acioss the grain is small compared with tension andcompression, (ireen wood shears much more easilv than dr^^ be-. Fii.,^. 43. Shearint,^ Slreng-th is Measured by the Adhesion of the Portion A, B, C, D or to the Wood on both sides of it. SiP FoiTstry liiillctin Nn. 7(t, pp. 11. \-l, iiinl Fovcstvv Cirrular No. 108. PROPERTIES OF WOOD. 53 cause moisture softens the wood and this reduces the adhesion of thefibers to each otlier/ CLEAVABILITY OF WOOD. Close!} connected with slieaiing strength is cohesion, a propertyusually considered under the name of its opposite, cleavability, i. e.,the ease of splitting. When an ax is stuck into the end of a piece of \yood, the woodsplits in advance of the ax edge. See Handwork in Wood, Fig. 59,p. 52. The wood is not cut but pulled across the grain just as trulyas if one edge were held and a weight were attached to the otheredge and it were torn apart by tension. The length of the cleftahead of the blade is determined by the elasticity of the wood. Thelonger the cleft, the easier to split. Elasticity helps splitting, andshearing strength and hard
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforests, bookyear1912
