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V. On the Strength of Ductile Materials under Combined 

 Stress. By James J . Guest *. 



Contents of Articles. 



1. Lack of knowledge of laws of strength. 



2. Separation of the isotropic materials into ductile and brittle. 



3. The yield-point in Tension Tests. 



4. The yield-point, rather than the ultimate, stress the criterion of 



strength. 



5. Variations of the ultimate and yield-point stresses : annealing. 



6. The elastic limit. 



7. The elastic-limit effect probably due to the existence of local yield- 



points. 



8. The yield-point, in preference to the elastic limit, selected as the 



criterion of strength. 



9. Torsion a case of combined stress. 



10. First reason for use of thin tubes as specimens. 



11. Results of previous torsion experiments. 



12. Previous experiments upon the yield-point under combined stress. 



13. Experiments upon ultimate strength under combined stress. 



14. Theories of elastic strength under combined stress : the maximum 



stress theory. 



15. The maximum strain theory. 



16. Theorem upon the limiting values of o\ 



17. The maximum strain theory not disproved by published experiments. 



18. The maximum shearing-stress criterion of elastic strength. 



19. Further reasons for adopting thin tubes as specimens. 



20. Range of stress covered by different types of experiment. 



21 . Method of checking the isotro pism of the material as regards yield-point 



stresses. 



22. Objections to tubes on account of want of isotropy. 



23. Objections to tubes on account of large effect of defects. 



24. The system of Tests. 



25. The specimens and holders. 



26. The tension loads. 



27. The application of torque. 



28. The friction of the torsion-rigging. 



29. The application of the internal pressure. 



30. Measurement of the fluid pressure. 



31 . A new type of pressure-gauge. 



32. Measurement of the distorsions. 



33. A new Extensometer. 



34. Errors of extensometer. 



35. A new twist-measuring apparatus. 



36. Proof that the torsion-mirrors measure the twist. 



37. Effect oi bending. 



38. As a transmission dynamometer. 



39. The diametral extensometer. 



40. Method of making the Tests. 



41. The determination of the sectional area and thickness of the tubes. 



42. Calculation of the stresses. 



43. Calculation of the strains. 



44. Maximum shear and slide are proportional. 



* Communicated by the Physical Society : read May 25th, 1900. _ 



