. A treatise on the mathematical theory of elasticity . * Several kinds of extensometers are described by Ewing and Unwin. t Unwin, loc. cit. X Bausohinger, Mittheilungen, xx. (1891). ip; STRESS-STRAIN DIAGRAMS [oh. IV downwards, so that the strain increases faster than it would do if it wereproportional to the traction; in this stage the strain is largely a permanentset. As the traction increases there comes a region of well-marked dis-continuity, in which a small increase of traction produces a large increaseof set. The traction at the beginning of this region is called the
. A treatise on the mathematical theory of elasticity . * Several kinds of extensometers are described by Ewing and Unwin. t Unwin, loc. cit. X Bausohinger, Mittheilungen, xx. (1891). ip; STRESS-STRAIN DIAGRAMS [oh. IV downwards, so that the strain increases faster than it would do if it wereproportional to the traction; in this stage the strain is largely a permanentset. As the traction increases there comes a region of well-marked dis-continuity, in which a small increase of traction produces a large increaseof set. The traction at the beginning of this region is called the a further considerable increase of traction the bar begins to thin downat some section, determined apparently by accidental circumstances, and thereit ultimately breaks. When this local thinning down begins the load isusually eased off somewhat before rupture occurs, and the bar breaks withless than the maximum traction. The maximum traction before rupture iscalled the breaking stress of the material, sometimes also the ultimatestrength or Fig. 8. Fig. 9. Figure 8 shows the character of the diagram for weld iron. It isreduced from one of Bauschingers curves. Similar diagrams for mild steelare drawn in many books. A is the limit of linear elasticity; between A andB the strain increases rather faster than between 0 and A and at a varyingrate, B is the yield point and D represents the maximum traction. Fig. 9is reduced from one of Bauschingers curves for cast iron. There is nosensible range, and so no limit, of linear elasticity, and no yield-point. Diagrams may be constructed in the same way for thrust and contraction,but the forms of them are in general different from the above. For someexamples of the determination of the yield-point under thrust reference maybe made to Bauschinger, Mittheilungen, xiii. In the case of cast iron it hasbeen verified that the curve is continuous through the origin, where there isan inflexion*. * See Ewing, loc. cit., p. 31. 77; 78
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