Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . Fig. 193. ELEMEXTARY STRESSES, ETC. 199 As an example of internal stress, consider again the case<of a rod in tension ; Fig. 193 shows the whole rod (or eye-bar) free, the forces P being the pressures of the pins inthe eyes, and causing external stress (compression here)on the surfaces of contact. Conceive a right section madethrough BS, far enough from the eye, (7, that we may con-sider the internal stres
Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . Fig. 193. ELEMEXTARY STRESSES, ETC. 199 As an example of internal stress, consider again the case<of a rod in tension ; Fig. 193 shows the whole rod (or eye-bar) free, the forces P being the pressures of the pins inthe eyes, and causing external stress (compression here)on the surfaces of contact. Conceive a right section madethrough BS, far enough from the eye, (7, that we may con-sider the internal stress to be uniform in this section, andconsider the portion BSG as a free body, in Fig. 194. Thestresses on BS, now one of the bounding surfaces of thefree body, must be parallel to P, , normal to BS;(otherwise they would have components perpendicular toP, which is precluded by the necessity of 17 being = 0,and the supposition of uniformity.) Let F = the sec- FlG. Fig. 195. tional area BS, and p = the stress per unit of area; then IX= 0 gives P= Fp, , p=? . (2) F The state of internal stress, then, is such that on planesperpendicular to the axis of the bar the stress is tensile andnormal (to those planes). Since if a section were madeoblique to the axis of the bar, the stress would still beparallel to the axis for reasons as above, it is evident thaton an oblique section, the stress has components both nor-mal and tangential to the section, the normal componentbeing a tension. 200 MECHANICS OF ENGINEERING. The presence of the tangential or shearing stress in ob-lique sections is rendered evident by considering that if anoblique dove-tail joint were cut in the rod, Fig. 195, theshearing stress on its surfaces may be sufficient to over-come friction and cause sliding along the oblique plane. If a short prismatic block is under the compressive ac-tion of two forces, each = P and applied centrally in onebase, we may show that the state of int
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectenginee, bookyear1888
