Benton — Experimental Method in the Flow of Solids. 207 



Art. XYIII. — An Experimental Method in the Flow of 

 Solids and its Application to the Compression of a Cube of 

 Plastic Material ; by J. R. Benton. 



When a solid body is subjected continuously to stress 

 beyond its elastic limit, so that a flow of the material takes 

 place, the behavior of its surface can be studied quite easily 

 by ruling lines upon it and observing how they are deformed ; 

 from such observations it has been possible to draw some con- 

 clusions about the flow in particular cases. The interior of 

 the body is much less accessible to experiment. Some infor- 

 mation about the flow in the interior of metals has been 

 obtained by comparing the " grain " of specimens which have 

 been strained beyond the elastic limit with that of similar 

 specimens which have not received such treatment;* but it is 

 not possible to observe the grain in the interior of the same 

 specimen both before and after flow, nor could this method be 

 applied to metals which do not show grain. Again, much 

 information has been obtained by building up bodies out of 

 plates of the substance to be investigated ; after the flow of 

 such a composite body, sections can be made through the 

 plates, and their form observed. This method can be used in 

 many particular cases ;f in many other cases (for example, in 

 studying the flow during flexure beyond the elastic limit) its 

 application would involve great practical difficulties. Besides 

 this there is a serious objection to it on theoretical grounds, on 

 account of the interruption of continuity of the body. And 

 although the method enables us to study the deformation of 

 surfaces in the body, it does not so readily furnish complete 

 information about the motion of individual points in those 

 surfaces. 



If instead of filling the body with a system of surfaces of 

 discontinuity, we fill it with a system of intersecting lines, 

 these objections can be overcome. Suppose that instead of 

 each surface of discontinuity, we introduce a framework con- 

 sisting of two sets of uniformly spaced parallel straight wires 

 at right angles to each other, all the points of intersection of 

 the wires being melted together. Such a framework, it is 

 true, would interfere with the continuity of the body to a 

 slight extent ; but much less so than if the body were built up 

 out of separate plates. Furthermore, it would give the means 

 of studying the motion of the individual points in the interior, 



*H. Tresca. Proc. Inst, of Mechanical Engineers, 1867, pp. 114-143; 

 1878, pp. 301-345. 

 f Loc. cit. 



