Kikuo Hosono

Stress Measurements By Strain Gages Made Of Nickel Foil

Strain gages made of nickel foil are developed for measuring the elastic surface stress of machine parts in operation. Sticking a piece of nickel foil about 10 um thick on the surface of a specimen subjected to repeated loads, the elastic stress is measured by observing slip-bands in the foil resulting from repeated strains. Calibration studies with rotating-bending tests are performed on round steel bars with nickel foil to determine the applicable test temperatures for the gage, and to establish the relation between the threshold stress for the first appearance of slip-bands and the number of stress cycles. The peak stresses in grooved shafts under bending are measured with the nickel foil gages, and the accuracy of the results is examined.

On the adaptability of the nickel electroplating method of stress analysis to variable test temperatures.

The adaptability of the electroplating method of stress analysis to variable test temperatures is examined by using nickel plating foil of 5 μm in thickness. The test temperatures vary gradually or stepwise in the range from 100°C to 200°C. The relations between the proper stress σp of the nickel plating foil and the number of stress cycles N, namely, the σp-N curves at variable test temperatures are obtained by the calibration tests in rotating bending in which N=(0.54.5)×106 cycles are designated. It is found that the σp-values at variable test temperatures can be estimated by using the formulas of the σp-N curves at constant temperatures, which is based on the assumption that the appearance of slip-bands in the nickel plating foil owing to cyclic straining is subject to the linear cumulative damage law.