Critical Bending Radius Research Articles

Transmission of optical radiation by sharp bends in fiber-optical waveguides

A theoretical and experimental investigation is reported of the behavior of optical radiation near single sharp bends in quartz multimode fiber-optical waveguides. The theory uses conformal mapping of complex-variable functions to transform a curved waveguide into a straight one. Allowance is made for spatial distortions of the electromagnetic fields at the bend. The experimental method uses the experimental observation that almost all (~ 80%) of the optical radiation which has escaped from the core into the cladding in the bend area, is returned to the core when the waveguide becomes straight again. The technique involves measuring the dependence of the optical radiation intensity at the exit from the bent waveguide on the variable refractive index of the external medium in which the bend is immersed. By using this technique, it is possible to determine experimentally the interval of the propagation constants of the cladding modes excited at the bend, the intensity of the residual radiation which does not leave the waveguide core for the given bend radius, and the critical bend radius for which all the core radiation escapes into the cladding in the bend area. The theory satisfactorily explains the results.

冷間加工された溶接構造用鋼板の時効と溶接による脆化

COD tests were conducted on JIS-SM41B, -SM50B and -SM58Q steel plates in order to examine the effect of strain-aging on embrittlement of these steels. Hot straining embrittlement phenomenon was also studied on weld joints of cold worked steel plates. Finally the bending radius allowable in cold working of structual steels was examined on the basis of COD test results.The main results obtained are as follows:(1) Strain-aging strongly affects the brittle fracture behavior and shifts the COD transition curve toward the higher temperature range. Fibrous crack initiation at the crack tip and its slow growth, on the other hand, are not strongly affected by strain-aging if the prestrain is limited up to 10%.(2) The amount of the shift of COD transition curve toward the higher temperature range due to strain-aging is in good accordance with the prediction based on the Tetelman's critical fracture stress theory.(3) The COD value at the hot straining embrittled zone near the weld joint of cold worked steel plate is nearly equal to that of the steel plate which is strained and then aged at 250°C for one hour.(4) The critical bending radius allowable in cold working can be calculated using the COD test results, and it is 4.57.3 times as large as the plate thickness.

Radiation from curved single-mode fibres

A study of propagation in curved single-mode fibres shows that the transmission loss increases sharply below a critical bend radius. However the radiation does not leak away uniformly with distance but in a series of discrete well-defined rays.