( 263 ) 



XIV. — Apparatus for Measuring Strain and Applying Stress, with an Account of some 

 Experiments on the Behaviour of Iron and Steel under Stress. By E. G. Coker, 

 D.Sc. Communicated by Dr C. G. Knott. (With Eight Plates.) 



(Bead 3rd June 1901.) 



CONTENTS. 



PAGE 



I. Introduction, 263 



II. Description of the Apparatus — 



1. Instrument for Measuring Strains, . 264 



2. Machine for applying Torque and 



Bending, 267 



3. Apparatus for applying Torque and 



Tension, 268 



III. Method op Experimenting, . . . 270 



IV. The Form of the Stress-strain Curve, 270 

 V. The Form of the Curve at the Yield- 

 point, 270 



VI. Recovery of Elasticity with Time, . 271 

 VII. The Position of the Yield-point as 



affected by previous Stress, . . 277 

 VIII. Twist in alternately opposite Direc- 

 tions, 277 



IX. The Influence of Tension on Torsion — 



1. Tension within the Elastic Limit, and 



Torsion within the Elastic Limit, 



2. Effect of Tensional Stress on the 



Yield-point, .... 



3. Tension beyond the Elastic Limit, 

 X. Effect of Torsion on Tension, 



XI. Effect of Bending on Torsion, . 



1. Bending within the Elastic 



and Torsion within the 

 Limit, 



2. Bending beyond the Elastic Limit, 



3. Effect of Bending upon the Yield 



point, 



XII. Effect of Annealing, . 



Limit, 

 Elastic 



page 



280 



282 

 283 

 285 



285 



286 

 286 



288 

 291 



I. — Introduction. 



The behaviour of metals under stress has long been the subject of investigation, 

 both by mathematicians and physicists, so that the laws of strength are tolerably 

 complete. Owing to the importance of iron and steel in construction, these materials 

 have been subjected to very extensive tests, particularly in simple tension and com- 

 pression. 



Numerous tests of cylindrical iron and steel bars in torsion are also available, the 

 bulk of these being tests to destruction of samples of material used in actual machines 

 and structures designed by engineers. In such tests scientific accuracy is not of much 

 importance, the chief consideration being the obtaining of sufficient data for use in 

 design. The most accurate torsional work upon iron and steel has been the work of 

 physicists, and nearly all their investigations have been conducted upon specimens of 

 very small sectional area ; the reasons for this, no doubt, being that such specimens in 

 the form of wires are easily obtainable, and of great uniformity in size and quality, while 

 large test pieces are costly to prepare, and, moreover, cause considerable difficulty in 

 testing, because of the magnitude of the forces involved. Owing to the mode of manu- 

 facture, the physical properties of wire often differ to a considerable extent from turned 



VOL. XL. PART II. (NO. 14). 2 R 



