ON STRESS DISTRIBUTION IN ENGINEERING MATERIALS. 465 



Stress Distribution in Engineering Materials. — Report of the 

 Corninittee, consisting of Professoi' J. Perry {Chairman), 

 Professors E. G. Coker and J. E. Petavel {Secretaries), 

 Dr. A. Barr, Dr. Chas. Chree, Mr. Gilbert Cook, Pro- 

 fessor W. E. Dalby, Sir J. A. Ewing, Professor L. N. G 

 FiLON, Messrs. A. E. Fulton and J. J. Guest, Dr. B. P. 

 Haigh, Professors J. B. Henderson, F. C. Lea, and 

 A. E. H. Love, Dr. W. Mason, Professor A. Eobertson, 

 Dr. F. Rogers, Mr. W. A. Scoble, Dr. T. E. Stanton, 

 Mr. C. E. Stromeybr, and Mr. J. S. Wilson, to report on 

 certain of the more complex Stress Distributions in Engineer- 

 ing Materials. 



[Plates V.-VIII.] 



Introduction. 



During the last five years many of the questions which had occupied 

 the attention of the Committee have proved to be of considerable practical 

 importance in connection with aircraft construction and engine design, 

 and they have formed the subject of careful investigations initiated by 

 the Air Board and the Navy. 



At the present date much of the information is still regarded as con- 

 fidential, but it is hoped to include a summary of this work in a subsequent 

 report of the Committee. 



The accurate determination of crippling load of struts is an important 

 factor in the correct design of an aeroplane. Information is required 

 with regard to struts of variable section, of uniform strength with or 

 without lateral or eccentric loads. The questions have been treated 

 theoretically by Barling, Cowley, Levy, Southwell, and Webb, and experi- 

 mentally by Coker, Dalby, Lea, Robertson, and Scoble. Important 

 investigations on the vibration of shafts and propellers have been made 

 by Berry, Fage, Grifl&th, JefEcott, Kerr, Morley, Southwell, and Webb, 

 and methods of calculating the critical speed in complex cases have been 

 solved. 



Investigations on repeated stress have been carried out by Fulton and 

 Lea, and also, in connection with several special problems, by various 

 members of the N.P.L. staff. The question of the distribution of stress 

 in wing structures of aeroplanes has also formed the subject of several 

 papers ; a summary of the work of Filon and Low is included in the present 

 report. 



In 1917 a very ingenious method of evaluating torsional and shearing 

 stress by means of soap films was developed by Taylor and Grifl&th, which 

 is an important advance on the earlier work of Prandtl ; some details of 

 this are given below. 



During the war a number of systematic inquiries into cases of failure 

 of various engine parts have been carried out by the R.A.F. A discussion 

 of the information obtained will, it is understood, be published in due 



