. Report upon the forestry investigations of the U. S. Department of agriculture. 1877-1898. Forests and forestry. Fig 98.—Relation of fiber stresses and distortions. S1- / 2 3 4-5678 &f/0^// Fig. 99 .—Distribution of internal stresses in a beam at rupture Experience in testing, however, has taught that when a piece of green wood is tested in compression it will undergo a great distortion after the maximum load has been applied without actually breaking down—in fact, while sustaining the same load. A piece tested in tension, on the other hand, breaks suddenlv as ?oon as the maximum load is
. Report upon the forestry investigations of the U. S. Department of agriculture. 1877-1898. Forests and forestry. Fig 98.—Relation of fiber stresses and distortions. S1- / 2 3 4-5678 &f/0^// Fig. 99 .—Distribution of internal stresses in a beam at rupture Experience in testing, however, has taught that when a piece of green wood is tested in compression it will undergo a great distortion after the maximum load has been applied without actually breaking down—in fact, while sustaining the same load. A piece tested in tension, on the other hand, breaks suddenlv as ?oon as the maximum load is applied. A beam in failing may, therefore, sustain an increasing load long after the extreme compression fiber Ms been loaded to its ultimate strength; the fibers on the compression side continue to be mashed down, while the neutral plane its lowered and the stress in the tension fiber increases until, very oftenin practice, the beam " fails in ; With these facts and / 2_3 4 S //I/ 6 7 T WOO „ 8 9 /O. T LBS // /2 observations before us it is possible to con- struct a diagram so that it will represent, approximately, at least, the distribution of internal stresses in a beam at rupture. (See fig. 100.) In this figure OA represents the position of neutral plane at time of rupture, OU the distortion in the extreme compression fiber, UC the stress on same fiber, OL the distor- tion in extreme tension fiber, and LT the stress on that fiber. It can readily be seen that the manner of breaking will influence slightly the form of this diagram. If the beam fails in com- pression before the tension fiber reaches its elastic limit the line OT will be straight as shown, otherwise the line will assume some such position as O^T, (diagram 99), in which I, is the elastic limit in tension. From the approximate distribution of internal stresses their relation to the external load may be determined. The two funda- mental equations—(1) that the sum of inter- nal stresses
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectforestsandforestry
